a<-"你好"
b<-"Hello World"
.hidden<-c

d<-c(1:10)
e<-factor(c("A","A","A","A","B","B","B","C","C","C"))
means<-tapply(d,e,mean)
means

f<-seq(from=1,to=20,by=2)
g<-rep(0,10)
df<-data.frame(d,e,f,g)
df